On the Cork Equatorial Telescope, kc. 355 
Now, it is evident, that if this apparatus remain as described 
it will act simply as a clamp or coupling between the two axes. 
If, however, it be required to produce a slight motion in the 
instrument, or (supposing the clock to be going, and carrying 
the instrument at its normal rate) a slight acceleration or re- 
tardation of the clock speed, it is only necessary to revolve the 
grooved disc in one direction or another, and the result is a 
differential movement between the two ends of the shaft. 
This movement of pulley P is affected by a cord passing round 
grooved pulley, and carried to observer at eye-end of telescope. 
Electrically controlled clock movement (Fig. 6 and 7). The 
driving clockwork of these equatorials may be described as con- 
sisting of two parts. 
Ist. A uniform motion clock which is controlled by a frictional 
governor, and which, used by itself, has been found to give re- 
sults equal to any other form of uniform motion clock, but 
which when very great accuracy for long periods is required is 
supplemented by 
2nd. A system of electric control, which the following figure 
and description will explain :— 
Fig. 6. 
Scien. Proc., R.D.S. Fr. 3, Vou, v. Z2B2 
